From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.3 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL,SUBJ_OBFU_PUNCT_FEW,SUBJ_OBFU_PUNCT_MANY autolearn=ham autolearn_force=no version=3.4.2 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by inbox.vuxu.org (OpenSMTPD) with SMTP id 99740dc6 for ; Thu, 30 Jan 2020 16:36:53 +0000 (UTC) Received: (qmail 25976 invoked by uid 550); 30 Jan 2020 16:36:51 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 16221 invoked from network); 30 Jan 2020 14:56:24 -0000 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Thu, 30 Jan 2020 08:56:03 -0600 From: Segher Boessenkool To: Rich Felker Cc: Sergei Trofimovich , musl@lists.openwall.com, libc-alpha@sourceware.org, gcc@gcc.gnu.org, toolchain@gentoo.org Message-ID: <20200130145603.GW22482@gate.crashing.org> References: <20200125105331.7c5d284b@sf> <20200125155424.GZ30412@brightrain.aerifal.cx> <20200130123351.GU22482@gate.crashing.org> <20200130133740.GB1775@brightrain.aerifal.cx> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200130133740.GB1775@brightrain.aerifal.cx> User-Agent: Mutt/1.4.2.3i Subject: Re: [musl] musl, glibc and ideal place for __stack_chk_fail_local On Thu, Jan 30, 2020 at 08:37:40AM -0500, Rich Felker wrote: > On Thu, Jan 30, 2020 at 06:33:51AM -0600, Segher Boessenkool wrote: > > On Sat, Jan 25, 2020 at 10:54:24AM -0500, Rich Felker wrote: > > > > To support smash stack protection gcc emits __stack_chk_fail > > > > calls on all targets. On top of that gcc emits __stack_chk_fail_local > > > > calls at least on i386 and powerpc: > > > > (Only on 32-bit -fPIC -msecure-plt, for Power). > > Right, but musl only supports the secure-plt ABI. Sure, it is the modern one. Still only for 32-bit -fPIC for musl, too. > > > There is a half-serious proposal to put it in crti.o which is always > > > linked too, but that seems like an ugly hack to me... > > > > Not *very* ugly, but it would be very effective, and no real downsides > > to it (or do you see something?) > > Well either the thunk has to be written in asm per-arch, or some ld -r > magic (which is fragile and something I don't want musl to depend on > since I know users will someday hit breakage and rightfully blame us > for using ld -r) to merge an asm source and C source. Or perhaps the > existing crti.s content could be moved to file-scope __asm__ included > in the C source file...that might be ok? At least for powerpc, the existing crti.s gets stuff inserted after (in both functions), and then closed off by crtn.s -- not something you want to do in C :-) GCC can just say to also use extra crti files -- see STARTFILE_SPEC. Many platforms do that already. > > On Power it is just the setting up itself that is costly (in the config > > where we have this _local thing). > > I think it'd be the same. We don't have a shortage of usable registers, that's what I was getting at. All the other arguments are similar, sure. > > > Absolutely not. libssp is unsafe and creates new vulns/attack surface > > > by doing introspective stuff after the process is already *known to > > > be* in a compromised state. It should never be used. musl's > > > __stack_chk_fail is safe and terminates immediately. > > > > Some implementations even print strings from the stack, it can be worse ;-) > > :-) It wasn't a joke, unfortunately. > > > Ideally, though, GCC would just emit the termination inline (or at > > > least have an option to do so) rather than calling __stack_chk_fail or > > > the local version. This would additionally harden against the case > > > where the GOT is compromised. > > > > Yeah, but how to terminate is system-specific, it's much easier to punt > > this job to the libc to do ;-) > > My ideas was __builtin_trap, although a slightly more hardened version > (that might make users unhappy? :) is inlining a syscall to > sigprocmask to mask SIGILL/SIGSEGV before the trapping instruction so > that termination occurs regardless of whether there's a signal handler > installed. I think we should make this a separate RTL pattern? Or a (noreturn) libgcc function? Anyway, let's talk in the PR :-) > > Open a GCC PR for this please? > > Filed as https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93509 Thanks! Segher